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\begin{equation*}\frac{D^2F(P_0)}{DP^2}=\frac{DF'(P_0)}{DP}=\frac{F'(P_1\!<\!P\!<\!P_2)-F'(P_0\!<\!P\!<\!P_1)}{\Delta P_i}\ne\frac{F'(P_1)-F'(P_0)}{\Delta P_i},\,\!\end{equation*}
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